1. Field of the Invention
The present invention relates to a hand-held device for whitening teeth, and more particularly, to such a device that has an actinic light applying tip with a reservoir for directly contacting a user's teeth with a whitening composition through which the actinic light passes.
2. Background of Invention and Related Art
Teeth can become discolored by chromogenic (color-causing) substances in food, beverages, tobacco, and salivary fluid, in addition to blood, amalgam restoratives, and antibiotics such as tetracycline. Tooth structures generally responsible for presenting a stained appearance are enamel, dentin, and the acquired pellicle. Tooth enamel is predominantly inorganic, mostly in the form of hydroxyapatite crystals, but it also contains approximately 5% organic material primarily in the form of collagen. Dentin is composed of about 20% protein including collagen, the balance consisting of inorganic material, predominantly hydroxyapatite crystals similar to those found in tooth enamel. The acquired pellicle is a proteinaceous layer on the surface of tooth enamel which re-forms rapidly after an intensive tooth cleaning.
Tooth stains may be either extrinsic or intrinsic, depending upon their location within the tooth structure. For example, extrinsic staining, of the acquired pellicle, arises as a result of compounds such as tannins and other polyphenolic compounds which become trapped in and tightly bound to the proteinaceous pellicle layer that spontaneously forms on the surface of the teeth. This type of staining can usually be removed by mechanical methods of tooth cleaning that remove all or part of the acquired pellicle together with the associated stain. On the other hand, intrinsic staining, of the enamel and/or dentin, can occur when chromogens or pre-chromogens penetrate and become tightly bound to these tooth structures. Intrinsic staining may also arise from systemic sources of chromogens or pre-chromogens, such as excess fluoride intake during enamel development, which can lead to the mottled yellow or brown spots typical of fluorosis staining. Intrinsic staining by its nature is not amenable to mechanical methods of tooth cleaning and generally requires the use of chemicals, such as hydrogen peroxide, that can penetrate into the tooth structure, in order to effect a change in the light absorptivity of the chromogens bound there. In general, intrinsic staining is more intractable and difficult to remove than extrinsic staining.
Given these two basic types of tooth staining, tooth cleaning approaches generally fall into two categories. One comprises the mechanical agitation of gels, pastes, or liquids, including toothpastes, at the tooth surface to effect extrinsic stain removal through abrasive erosion of the stained acquired pellicle. The other, particularly adapted for mitigating intrinsic staining, comprises contacting the tooth with a formulation typically comprising a gel, paste, or liquid that accomplishes a chemical bleaching effect while in contact with the stained tooth surface for a specified period (with or without the application of mechanical cleaning action), after which the formulation is removed. In some cases, an auxiliary chemical process or additive, which may be oxidative or enzymatic, supplements the mechanical process.
The most effective bleaching compositions contain an oxidizing agent, such as hydrogen peroxide, that attacks the bound chromogen molecules in such a way as to render them colorless, water-soluble, or both. In one popular approach a dental professional constructs a custom-made tooth-bleaching tray for the patient from an impression of the patient's dentition. On his or her own, the patient dispenses a prescribed oxidizing gel into the tooth-bleaching tray and wears it repeatedly for several minutes or hours at a time over a period ranging from about two weeks to six months, depending upon the severity of tooth staining. These oxidizing compositions, usually packaged in small plastic syringes, are dispensed directly by the patient into the custom tooth-bleaching tray and held in place in the mouth typically for an hour or more, sometimes up to eight to 12 hours in certain treatment regimens. The slow rate of bleaching is in large part the consequence of the very nature of the formulations that have been developed to maintain stability of the oxidizing composition. The most commonly used oxidizing compositions contain the hydrogen peroxide precursor carbamide peroxide mixed with an anhydrous or low water content, hygroscopic viscous carrier containing glycerin and/or propylene glycol and/or polyethylene glycol. When contacted by water, carbamide peroxide dissociates into urea and hydrogen peroxide. The slow rate of bleaching in this prior approach using a hygroscopic carrier has proven to cause tooth sensitization in over 50% of patients. This tooth sensitivity is believed to result from the movement of fluid through the dentinal tubules, which is sensed by nerve endings in the tooth. Worse, the carriers for the carbamide peroxide enhance this movement. In fact, it has been determined that glycerin, propylene glycol, and polyethylene glycol all can give rise to varying amounts of tooth sensitivity following exposure of the teeth to heat, cold, overly sweet substances, and other causative agents.
This kind of prolonged exposure of teeth to bleaching compositions has a number of other adverse effects in addition to causing tooth sensitivity. These include: solubilization of calcium from the enamel layer at a pH less than 5.5, with associated demineralization of the enamel; penetration of the intact enamel and dentin by the bleaching agents, which if they reach the pulp chamber of a vital tooth risk damage to pulpal tissue; and dilution of the bleaching composition with saliva, resulting in leaching of the composition from the dental tray and subsequent ingestion by the patient, not to mention reducing the efficacy of the bleaching process.
An alternate approach uses oxidizing compositions (generally with relatively high concentrations of oxidizers) that are applied directly to the tooth surface of a patient in a dental office under the supervision of a dentist or dental hygienist. Theoretically, such tooth whitening strategies have the advantage of yielding faster results and better overall patient satisfaction; however, due to the high concentration of oxidizing agents contained in these so-called “in-office” or “chairside” compositions, they can be hazardous to the patient and practitioner alike if not handled with care. The patient's soft tissues (the gingiva, lips, and other mucosal surfaces) must first be isolated from potential exposure to the active oxidizing agent by the use of a perforated rubber sheet (known as a rubber dam), through which only the teeth protrude. Alternatively, the soft tissue may be isolated from the oxidizers to be used in the whitening process by covering the tissue with a polymerizable composition that is shaped to conform to the gingival contours and subsequently cured by exposure to a high intensity light source. Applying these rubber dams and polymerizable compositions typically requires significant skill on the part of the clinician and can take up to 20 minutes. Once the soft tissue has been isolated and protected, the practitioner applies the oxidizing agent directly onto the stained tooth surfaces for a specified period of time or until a sufficient change in tooth color has occurred, sometimes applying heat to enhance the bleaching action of the oxidizing composition. This approach yields satisfactory results, typically producing between five to nine shades of improvement in tooth whiteness (as measured with the VITA® Shade Guide, VITA Zahnfarbik, Bad Sackingen, Germany).
The VITA® Shade Guide used as standard for measuring tooth whiteness assigns shades from very light (B1) to very dark (C4). A total of 16 VITA® shades constitutes the entire range of colors between these two endpoints on a scale of brightness, and tooth whitening is often judged by the number of shade changes achieved. Professional whitening procedures can in some cases achieve a brightness increase of four or five VITA® shades, but a change as small as one to two shades will be noticed by most patients. Accordingly, the improvement of five to nine shades using the approach discussed in the previous paragraph can be considered a good result, but the procedure is time-consuming because it involves so many complicated steps, is expensive and inconvenient because it can only be performed by a dental professional in an office setting, and can be dangerous if it includes the application of heat (for reasons discussed in more detail below). Since most patients can notice a change of only one or two VITA® shades, many individuals would accept simpler, cheaper, more convenient, and safer alternatives, even if they did not improve tooth brightness as much as procedures using chairside compositions requiring professional application.
It is known that applying actinic radiation such as heat (infrared), discussed above, to the teeth during bleaching, particularly when the bleaching composition is a peroxide, speeds and enhances the whitening process. “Actinic radiation” refers to light energy capable of being absorbed by a tooth stain chromogen, or capable of accelerating the oxidation of a tooth stain chromogen in the presence of an oxidizing agent. The term actinic radiation may also mean light energy capable of accelerating chemical reactions in general. The terms “actinic radiation” and “actinic light” may be used interchangeably in this description. Known procedures involve the application of actinic light in ultraviolet and/or infrared wavelengths. Again, such methods can be effective for whitening teeth, but ultraviolet light can be hazardous to the patient and practitioner alike and infrared radiation may damage tooth structures and/or burn the patient unless precautions are taken.
U.S. Pat. No. 4,952,143 attempts to address these drawbacks with a dental bleaching instrument for use by a professional that filters out ultraviolet wavelengths and has a temperature regulation mechanism that involves placing a temperature sensor at the tooth surface to provide a feedback control mechanism to prevent excessive temperatures. However, that does not solve the basic problem that using heat at all can risk tooth damage, which means that this approach can be used only under the close supervision of a professional with the proper equipment. Even then, it still poses risks to tooth structures, especially in patients whose teeth may be prone to damage from heat.
A related technique is discussed in U.S. Pat. No. 5,032,178, which discloses compositions and methods that purportedly improve tooth whitening efficacy by using exposure to optical energy in the visible spectrum wavelength range of 400 to 700 nanometers. The compositions disclosed in this patent require the use of an aqueous solution of hydrogen peroxide with (1) an inert silica gelling agent, (2) a catalytic accelerator (either manganese sulfate monohydrate or ferrous sulfate), (3) an agent for providing thixoplasticity and thickening properties to the composition, such as cellulose ethers and methyl vinyl ethers, and (4) a redox color indicator, which indicates completion of the bleaching treatment of the teeth by transforming from one color to another in response to the dissociation of hydrogen peroxide over a given time period. The described compositions are combined into a homogeneous mixture prior to use with all of the required components dispersed evenly throughout the mixture. The compositions are not particularly transparent to light energy in the range of 400 to 700 nm because the inorganic silica particles inhibit light energy from reaching the tooth surface where it can act to sensitize chromogens in the tooth structures to the oxidizers in the mixture. Indeed, commercial mixtures based on this patent (available under the trade name Shofu Hi-Lite® from Shofu Dental Corporation, Menlo Park, Calif.) are nearly opaque. Typical results obtained using such compositions and methods are about two to three VITA® shades improvement in tooth color, similar to that achieved with compositions that do not employ light energy in the process of bleaching teeth. Thus, even though this approach uses visible light instead of ultraviolet or infrared radiation, the light seems to have little effect, and the procedure must be done by a dental professional.
A commercial product called Opalescence® Xtra® available for bleaching teeth in the controlled environment of a dental office has been introduced by Ultradent Products, Inc., South Jordan, Utah. U.S. Pat. No. 5,785,527 is believed to describe this product. The commercial product is supplied in a plastic syringe and is described in accompanying literature as a light-activated tooth whitening gel, which contains approximately 35% hydrogen peroxide. A pH determination showed the product to have a neat pH of about 4.0 at 25° C. The product is thickened to a loose, gel-like consistency with a polymer. Additionally, the product as sold, and as described in U.S. Pat. No. 5,785,527, contains a bright orange pigment or dye (carotene), claimed to be a photosensitizer that absorbs light energy and converts it to heat, thereby increasing the activity of the peroxide as a tooth bleaching agent. Indeed, the presence of a photoabsorber renders the composition relatively opaque to visible light at wavelengths from about 400 to 700 nm, which thus would not reach the tooth surface in a meaningful amount. Comparative clinical results show an improvement in tooth color of from about three to four VITA® shades, which is significant, but appears to depend more on the time of the composition remains in contact with the tooth surface, rather than any particular light or heat activation regimen. In addition, the low pH of the commercial product may cause a reduction in the microhardness of tooth enamel, due to the dissolution of hydroxyapatite crystals (which can occur at a pH of around 5.5 or less).
Devices for use in light/heat-activated tooth whitening procedures also include the commercially available Union Broach® Illuminator System, from Union Broach, a Health/Chem. Company. New York. N.Y. This device, as described by the manufacturer, provides direct, full spectrum illumination to all of the teeth found in the front of the average adult's mouth. The Union Broach light is used in conjunction with a 35% hydrogen peroxide solution (Superoxol), which requires a dental professional to apply to the teeth prior to and during illumination with the light source. However, this device does not uniformly illuminate all sixteen central teeth in the front upper and lower arches because of the curvature of the dentition. This potentially gives rise to uneven results. In addition, the Union Broach device generates a great deal of heat which is both uncomfortable for the patient and potentially damaging to the teeth, as already mentioned.
Commercially available professional teeth whitening devices that successfully and safely use light to enhance the removal of teeth stains are available. Most of these professional devices are LED projector-type tooth whitening devices which are designed to project high intensity actinic light from an emitting surface, typically an array of LEDs or other optical outputs. Professional light emitting devices typically emit in excess of 100 milliwatts per square centimeter of actinic light. Examples of successful professional tooth whitening devices include the Zoom® In-Office Whitening Lamp and the BriteSmile® whitening device (both sold by Discus Dental LLC, a division of Philips Oral Healthcare, Los Angeles, Calif.). These devices are maneuvered by the professional such that when positioned inside or just outside the mouth of the patient in close proximity to tooth surfaces, all of the “smile-line” teeth (8-10 uppers and 8-10 lowers) are exposed to actinic light at the same time. Since projector-type tooth whitening devices illuminate all of the patient's teeth and gum surfaces simultaneously, the soft tissues must be isolated and protected from exposure to the high intensity light to prevent possible damage. Typical isolation materials, such as those described in U.S. Pat. No. 6,048,202 and U.S. Pat. No. 6,800,671, are applied in liquid, gel, or paste form and subsequently polymerized to form the necessary isolation barrier before the tooth whitening procedure and exposure to light can begin. This can be a time-consuming and uncomfortable process for the patient.
These and other prior art tooth whitening devices and methods that use actinic radiation are all somewhat inconvenient to use because they require the intervention of a professional. They also demonstrate varying degrees of efficacy and safety, and in some cases can actually harm the teeth and soft tissues of the mouth if the professional using them fails to adhere strictly to proper procedures designed to prevent such damage. As a result, an effective manner of chemical tooth bleaching, that safely and effectively employs the enhancing action of actinic radiation in a form that presents a lesser risk of tooth damage and that does not require the involvement of a professional, would be highly advantageous.
The prior art does disclose some hand-held tooth whitening devices that apply actinic radiation and are designed for consumer use. Some examples are U.S. Pat. No. 6,056,548 and, more recently, Patent Pub. No. US2005/0026103 and No. US2011/0123958. The latter has an applicator head with a reservoir for a photoactivatable composition, and the reservoir has a cover through which the composition is extruded onto a treatment surface or, for its tooth bleaching embodiment, an absorbent pad such as a sponge in the reservoir holds the composition and is used to rub the tooth surface. Actinic radiation, produced by an LED, must pass through the sponge containing the photoactivatable composition.
While Patent Pub. No. US2011/0123958 describes a hand-held device meant to use actinic radiation for tooth whitening, the efficacy of the device as disclosed may be compromised by a number of factors. For one thing, the amount of actinic radiation available at the tooth surface will inevitably be attenuated by the sponge, and the photoactivatable composition absorbed in the sponge will by definition absorb actinic radiation passing through it and thus even further reduce the amount of radiation actually reaching the tooth surface. Even so, there may still be sufficient energy to present a hazard if the user inadvertently directs the light from the LED at his or her eye while using the device. Nor does there appear to be any mechanism for preventing exposure of soft tissues in the user's mouth from stray actinic radiation.
Home-use devices for applying actinic light in conjunction with tooth whitening compositions are commercially available in the form of actinic light emitting mouthpieces and projectors to illuminate all of the smile-line teeth at the same time. A serious drawback to these products is their inability to achieve levels of light intensity at the tooth surface during use required to accelerate the elimination of tooth stains because to do so would expose surrounding soft tissues to excess radiation. That is, illumination of lips and gums with high intensity actinic light can cause burns and thus is a limiting factor to the intensity of light that can be emitted safely from mouthpieces that use LEDs as the actinic light source. An example of a commercially available LED-illuminated mouthpiece is the GloBrilliant® Teeth Whitening Device (GloScience, New York, N.Y.), which emits light energy at less than 40 milliwatts per square centimeter when measured under simulated usage conditions. Examples of projector-type teeth whitening devices include the GoSmile® Smile Whitening Light (GoSmile Inc, Berkeley, Calif.) and the Luster® 1-Hour White® teeth whitening device (Dentovations, Boston, Mass.). Both of these devices also emit light energy at less than 40 milliwatts per square centimeter when measured under simulated usage conditions.
There is thus a need for improved methods and devices for whitening teeth using oxidizing agents and actinic energy of safe wavelengths and sufficient power density to enhance and speed whitening. In particular, there is a need for tooth whitening methods and devices capable of whitening teeth quickly, easily, and safely, and that limit the ability of the user to apply the actinic radiation to areas other than intended, eliminate the risk of harming tooth enamel, dentin, pulp or soft tissues in the oral cavity, can be adapted for consumer use, and apply an oxidizing agent to the teeth in the minimum amount necessary for effective bleaching of the tooth surface while limiting exposure of soft tissues to the oxidizing agent.